The problem of pain created in hypersensitive areas of dentin and cementum is quite common. The pain can be created in response to various stimuli on the surface of the teeth, such as thermal changes, changes in pH, contact with a brush or dental instrument, and other common circumstances which are difficult to avoid. The problem is especially acute in patients who have lost some of the normal protective enamel sheathing on tooth surfaces because of erosion, abrasion, caries, chipping of the enamel, or exposure of the dentin and cementum as a result of recession of the gums.
While the cause of pain from hypersensitive dentin or cementum has not been completely explained, a number of theories have been postulated. It is believed, however, that the cause of sensitivity is the degree of openness of the tubules in the area. It is postulated that displacement of the contents of the tubules under various conditions, as by contact of dentin with an air jet, scraping with a probe, temperature variation, or the application of a hypertonic solution causes the transmission of pain stimuli by a hydrodynamic flow to the nerve structure located in the pulp area. The link in the transmission of the stimuli is fluid in the tubules within the dentin, and in this connection, a relatively rapid movement of fluid outwardly from the pulp has been most clearly associated with pain.
In the past, there have been two approaches in attempts to solve the problem of eliminating pain in hypersensitive areas of the dentin and cementum. One method involves occluding the tubules by salt formation from an organic or inorganic acid, or other means intended to block the transmission of neural impulses from the dentinal surface to the dental pulp. U.S. Pat. No. 3,122,483 discloses the use of strontium ions for adsorption at the surface of odontoblastic fibrils or in the dentinal tubules to block the transmission of neural impulses. U.S. Pat. No. 3,863,006 discloses the use of potassium, lithium or sodium nitrites, in the form of an aqueous solution or a paste, for desensitizing hypersensitive dentin or cementum. U.S Pat. No. 4,057,621 discloses the use of mono- or di-substituted salts of an alkali metal or ammonium oxalate for desensitizing hypersensitive cementum. The salts are applied as an aqueous solution or a nontoxic paste.
As an alternative to sealing the dentinal tubules with salts some attempts have been made to use polymeric materials as a sealing medium. This expedient has met with only limited success, however, since it is very difficult to achieve adhesion of a polymeric film to living tissue such as dentin, especially under the moist conditions which exist in the mouth.